Liquid cryogens are used in a number of industrial processes. For example, liquid nitrogen droplet dispensers are currently used to provide an inert head space when packaging oxygen sensitive products such as coffee and peanuts. Liquid nitrogen dispensers are also used in the packaging of carbonated beers and soft drinks in cans to provide both an inert head space and for increasing the rigidity of the cans.
Each application of a liquid cryogen usually requires a particular droplet size and, when installed on a production line, for example, a canning line, it is important that the size of the droplet being dispensed is constant since a varying droplet size will lead to a great variation in can pressure.
European Patent Publication No. 0331287 discloses an apparatus for dispensing a cryogenic liquid which includes a reservoir having an electrically heated dispensing tube connected to the bottom of the reservoir. Liquid cryogen contained within the reservoir is metered by an electrically controlled solenoid valve which, when activated, closes off the dispensing tube. The dispensing tube is electrically heated so that liquid cryogen within the dispensing tube undergoes film boiling. The film boiled liquid cryogen within the dispensing tube acts to lubricate slugs of liquid cryogen that are dispensed from the dispensing tube when the solenoid valve is raised.
Cryogenic liquid dispensers incorporating a solenoid valve and a heater are relatively cumbersome and expensive. Furthermore, they cannot achieve the mass flow and dosing rates often required by industry.
It is an aim of the present invention to provide an apparatus for dispensing a liquid cryogen which does not incorporate a separate solenoid valve and heater.